chore(protocol): only allow enc. password changes on cluster config (#10145)

In practice we already always call SetPassword and ClusterConfig
together. However it's not just "sensible" to do that, it's required: If
the passwords change, the remote device needs to know about that to
check that the enc. setup is valid/consistent (e.g. tokens match,
folder-type is appropriate, ...).
And with the passwords set later, there's no point in adding them as
part of creating a new connection.

This is a "followup" (if one can call it that 4 years later :) ) to
resp. fix for the following commit:
924b96856f

Co-authored-by: Jakob Borg <jakob@kastelo.net>

lib/model/requests_test.go

@@ -1240,7 +1240,7 @@ func TestRequestIndexSenderClusterConfigBeforeStart(t *testing.T) {
 		}
 		return nil
 	})
-	fc.ClusterConfigCalls(func(cc *protocol.ClusterConfig) {
+	fc.ClusterConfigCalls(func(cc *protocol.ClusterConfig, _ map[string]string) {
 		select {
 		case ccChan <- cc:
 		case <-done: